I posted this link a few posts back:
http://www.cancercare.ns.ca/media/document
s/Fact_sheet_Pap_Test_Rules_Change.pdf
Which explains this:
When should I have my first Pap test?
Women should have their first Pap test within three years of becoming sexually active, or at age 21, whichever comes first.
Why is it safe to wait for three years after the onset of sexual activity before having a first Pap?
A Pap test is done to see if there are pre-cancerous (dysplastic) or, more rarely, cancerous cells (invasive cervical cancer) on a woman’s cervix. Cervical cancer is caused by the human papillomavirus (HPV) and the virus is usually spread by sexual contact. HPV is usually cleared from the body naturally and causes no problem but sometimes the virus will stay in the body and cause genital warts or, over a long period of time, cervical cancer. Because invasive cervical cancer takes a long time to develop after exposure to HPV, experts say that screening can safely be delayed until three years after becoming sexually active.